A blackbody is an object that emits a mixture of electromagnetic radiation with a spectral content described by a statistical function called Planck's blackbody function. The spectral peak of this blackbody function is proportional to the absolute temperature (°K). The area under the blackbody function curve is proportional to the absolute temperature to the fourth power, and is proportional to the total power radiated by the blackbody.
Perfect blackbodies do not exist in nature, but blackbody devices can be built that closely emulate the radiant emittance of a blackbody over a limited spectral band and temperature range. A typical blackbody device includes an electrical heater element inside an insulated cavity. Blackbody devices have spectral radiance distributions that are easily calculated once the temperature is known and are therefore often used to calibrate infrared thermal cameras and other such imagers.
Blackbody devices that operate above ambient temperature are fairly easy to construct. However, due to very strong temperature dependence of the emitted spectrum of a blackbody device, when operated at low temperatures, the emissions are so small that they are very susceptible to contamination by reflected radiation from the surrounding warm environment as well as any self-emission from any intervening windows.
Prior art devices incorporate a cold, high-emissivity cavity or object (e.g., cold plate) in a thermally-shielded vacuum environment. The vacuum environment prevents frost accumulation, but it also necessitates locating the sensor inside the vacuum environment, or using an optical window which is transparent in the infrared range of the sensor. Accordingly, known low temperature blackbody devices are difficult to design and expensive to build.
Accordingly, it is desirable to provide improved low-temperature, adjustable blackbody systems that reduce stray thermal radiation from the surrounding environment, reduce frost build-up, are portable, easy-to-use, and reduce the effects of any window materials. Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.